共查询到20条相似文献,搜索用时 15 毫秒
1.
A method for calculation matrix-elements of the density operator for the superposition of two electromagnetic fields from the matrix-elements of the two components is developed. In the special case of superposition of a stationary coherent field and a stationary chaotic field results are compared with Peina's results. 相似文献
2.
This paper presents a quantum mechanical formalism of the classical coherence theory, within which the generalized radiance function defined in the time domain is regarded as a phase space representative of a time-dependent correlation operator of a polychromatic field. The theory deals with both stationary and nonstationary fields and, for a stationary field, provides a new operator formalism of the usual theory of optical coherence developed in the space-frequency domain. New results include an operator representation of the mutual coherence function, an operator version of the Wiener-Khintchine theorem, and an operator theorem that projects the correlation operator of a polychromatic field onto a particular spectral component. As illustrative examples, the previous formulas regarding the relationship between temporal coherence and spatial coherence, and the relationship between spectral properties and coherence properties are derived from the new operator formulas. The correspondence of the present formalism to the usual formalism using Dirac notation to describe the propagation of a stationary, partially coherent, quasi-monochromatic field is also considered. 相似文献
3.
S. Mudaliar 《Waves in Random and Complex Media》1999,9(4):521-536
This paper deals with scattering from a random-medium layer with rough boundaries. The fluctuations of the surface heights and medium permittivity are assumed to be small and smooth. All random quantities are assumed to be stationary and independent of each other. After the introduction of approximate boundary conditions, the system of partial differential equations is transformed into an integral equation where the fluctuations of the problem are represented as a zero-mean random operator. Employing smoothing, integral equations for the coherent fields are obtained. Use of the Helmholtz operator leads to solution for the coherent propagation constant while the boundary operators lead to coherent Fresnel coefficients. The characteristics of the results are illustrated by considering several examples. 相似文献
4.
We find that a squeezing transformation can efficiently simplify the density operator equation of field damping in a squeezed
bath. Then the entangled state representation is introduced to solve the simplified equation and the time evolution of density
operator, which turns out to be a mixed coherent squeezed state.
Work supported by the President Foundation of Chinese Academy of Science and Specialized research fund for the doctorial progress
of Higher Education (SRFDP). 相似文献
5.
Dynamical nonlocality of the entangled coherent state in the phase damping model 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper studies the dynamics of nonlocality for a bosonic
entangled coherent state in a phase damping model. The density
operator of the system is solved by using a superoperator method.
The dynamics of nonlocality for the bosonic entangled coherent state
is uncovered by the Bell operator based on the pseudospin operator
of a light field. The dynamics of the nonlocality for this state has
also been studied by other Bell operators. The result of the
numerical calculations of the Bell function shows that the quantum
nonlocality heavily depends on the chosen Bell operator. 相似文献
6.
In the quantum information theory operates with qubits and N-qubits that can be express through coherent states. Density operator admits a representation in terms of coherent states formalism. Consequently, in this paper the notions of qubit and density operators are described in the framework of coherent states. We have expressed a qubit as a coherent state, and thus a sequence of qubits becomes the tensor product of the coherent states. For the ensembles of qubits, it could be used the density operator, in order to describe the informational content of the ensemble. The coherent states representation may play an important role in the quantum information theory and the use of this formalism is not only theoretical, but also, due to its applications, of some practical relevance. 相似文献
7.
Fox RF 《Chaos (Woodbury, N.Y.)》1998,8(2):462-465
Gibbs entropy is invariant for the Baker map. A Jordan basis spectral decomposition of the Baker Frobenius-Perron operator suggests that any initial density evolves to the stationary density that has maximal entropy. This entropy conundrum is resolved by considering the difference between weak and strong convergence. A binary representation is used to make these points transparent. (c) 1998 American Institute of Physics. 相似文献
8.
H. Dekker 《Optics Communications》1974,10(2):114-119
Starting from a multimode hamiltonian for a system of radiating oscillators coupled with atomic reservoirs, the secular master equation for the radiation-density operator is calculated in the interaction picture after elimination of the atomic variables. Using the differential operator representation for coherent states this equation is transcribed into a multimode Fokker-Planck equation. The stationary solution in momentum space is given for the threshold region. Fourier transformation to configuration space results in a quasi-free energy formula for a laser oscillator exhibiting spatial dispersion. 相似文献
9.
Jeong Ryeol Choi 《中国物理C(英文版)》2011,35(3)
The time evolution of vacuum energy density is investigated in the coherent states of inflationary universe using a linear invariant approach. The linear invariants we derived are represented in terms of annihilation operators. On account of the fact that the coherent state is an eigenstate of an annihilation operator, the wave function.in the coherent state is easily evaluated by solving the eigenvalue equation of the linear invariants. The expectation value of the vacuum energy density is derived using this wave function.Fluctuations of the scalar field and its conjugate momentum are also investigated. Our theory based on the linear invariant shows that the vacuum energy density of the universe in a coherent state is decreased continuously with time due to nonconservative force acting on the coherent oscillations of the scalar field,which is provided by the expansion of the universe. In effect, our analysis reveals that the vacuum energy density decreases in proportion to t-β where β is 3/2 for radiation-dominated era and 2 for matter-dominated era. In the case where the duration term of radiation-dominated era is short enough to be negligible, the estimation of the relic vacuum energy density agrees well with the current observational data. 相似文献
10.
Jeong Ryeol Choi 《中国物理 C》2011,35(3):233-242
The time evolution of vacuum energy density is investigated in the coherent states of inflationary universe using a linear invariant approach. The linear invariants we derived are represented in terms of annihilation operators. On account of the fact that the coherent state is an eigenstate of an annihilation operator, the wave function in the coherent state is easily evaluated by solving the eigenvalue equation of the linear invariants. The expectation value of the vacuum energy density is derived using this wave function. Fluctuations of the scalar field and its conjugate momentum are also investigated. Our theory based on the linear invariant shows that the vacuum energy density of the universe in a coherent state is decreased continuously with time due to nonconservative force acting on the coherent oscillations of the scalar field, which is provided by the expansion of the universe. In effect, our analysis reveals that the vacuum energy density decreases in proportion to tβ where β is 3/2 for radiation-dominated era and 2 for matter-dominated era. In the case where the duration term of radiation-dominated era is short enough to be negligible, the estimation of the relic vacuum energy density agrees well with the current observational data. 相似文献
11.
Dušan Popov Ioan Zaharie Vjekoslav Sajfert Ioan Luminosu Deian Popov 《International Journal of Theoretical Physics》2008,47(5):1441-1454
In this paper we have showed that the qubit can be expressed through the coherent states. Consequently, a message, i.e. a sequence of qubits, is expressed as a tensor product of coherent states. In the quantum information theory and practice, only the code and key message are expressed as a sequence of qubits, i.e. through a quantum channel, the properly information will be transmitted by using a classical channel. Even if the most used coherent states in the quantum information theory are the coherent states of the harmonic oscillator (particularly, expressing by them the Schrödinger “cat states” and the Bell states), several authors have been demonstrated that other kind of coherent states may be used in quantum information theory. For the ensembles of qubits, we must use the density operator, in order to describe the informational content of the ensemble. The diagonal representation of the density operator, in the coherent state representation, is also useful to examine the entanglement of the states. 相似文献
12.
Dušan Popov 《Czechoslovak Journal of Physics》2002,52(9):993-1010
In the paper we construct a new set of coherent states for a deformed Hamiltonian of the harmonic oscillator, previously introduced by Beckers, Debergh, and Szafraniec, which we have called the BDS-Hamiltonian. This Hamiltonian depends on the new creation operator a
+, i.e. the usual creation operator displaced with the real quantity . In order to construct the coherent states, we use a new measure in the Hilbert space of the Hamiltonian eigenstates, in fact we change the inner product. This ansatz assures that the set of eigenstates be orthonormalized and complete. In the new inner product space the BDS-Hamiltonian is self-adjoint. Using these coherent states, we construct the corresponding density operator and we find the P-distribution function of the unnormalized density operator of the BDS-Hamiltonian. Also, we calculate some thermal averages related to the BDS-oscillators system which obey the quantum canonical distribution conditions. 相似文献
13.
V Balakrishnan 《Pramana》1979,13(4):337-352
A phenomenological interpolation model for the transition operator of a stationary Markov process is shown to be equivalent
to the simplest difference approximation in the master equation for the conditional density. Comparison with the formal solution
of the Fokker-Planck equation yields a criterion for the choice of the correlation time in the approximate solution. The interpolation
model is shown to be form-invariant under an iteration-cum-rescaling scheme. Next, we go beyond Markov processes to find the
effective time-development operator (the counterpart of the conditional density) in the following very general situation:
the stochastic interruption of the systematic evolution of a variable by an arbitrary stationary sequence of randomizing pulses.
Continuous-time random walk theory with a distinct first-waiting-time distribution is used, along with the interpolation model
for the transition operator, to obtain the solution. Convenient closed-form expressions for the ‘averaged’ time-development
operator and the autocorrelation function are presented in various special cases. These include (i) no systematic evolution,
but correlated pulses; (ii) systematic evolution interrupted by an uncorrelated (Poisson) sequence of pulses. 相似文献
14.
15.
Ana-Camelia?P?rghie Ciprian?Dariescu Marina-Aura?Dariescu 《International Journal of Theoretical Physics》2010,49(1):98-109
Projecting the closed form expression of the de Sitter scalar field operator onto the Minkowskian positive frequency massless
modes, we compute the corresponding Bogolubov coefficient which is associated to the (massless) quasiparticle creation during
the stationary quasi-de Sitter stage of the Universe. Thereafter, we derive the expression of the thermalized energy density
which reveals an interesting mixture of de Sitter false vacuum and dark-radiation, exotic dust and black body radiation. Setting
the temperature to the value of the Hawking one for the de Sitter spacetime, we finally analyze the (straightforward) back-reaction
of the newly created “matter” on the scale function. It basically points out three stages of highly continuous evolution represented
by an initially short radiation-like era, a somewhat long-lasting connecting phase made of coherent massless oscillations,
in its beginnings, ended up by the dark-radiation (i.e. curvature-like term) contribution and, finally, a much slower exponential
expansion than the initial de Sitter one. 相似文献
16.
An exact equation is derived for the evolution of the density operator in the coherent state representation describing spontaneous emission from a system of harmonic oscillators. 相似文献
17.
A spectral decomposition of the Frobenius–Perron operator is constructed for one-dimensional maps with intermittent chaos, using the method of coherent states. A technique using the spectral density function is applied to the the well-known cusp map, which generates weak type-II intermittency. Higher-order corrections are obtained to the leading 1/t long-time behavior of the x–x autocorrelation. 相似文献
18.
Evolution formulas of the density operator, the photon number distribution, and the Wigner function are derived for the problem on the optical fields propagation in realistic environments. Using the idea “reservoir modeled by beam splitter (BS)” and the Weyl expansion of the density operator, we obtain these formulas cleverly, which are very useful for quantum optics and quantum statistics. As an application, we study the time evolution of the photon number distribution and the Wigner function for single-photon-added coherent state in thermal environment. 相似文献
19.
We analyze traces of powers of the time evolution operator of a periodically kicked top. Semiclassically, such traces are related to periodic orbits of the classical map. We derive the semiclassical traces in a coherent state basis and show how the periodic orbits can be recovered via a Fourier transform. A breakdown of the stationary phase approximation is detected. The quasi energy spectrum remains elusive due to lack of knowledge of sufficiently many periodic orbits. Divergencies of periodic orbit formulas are avoided by appealing to the finiteness of the quantum mechanical Hilbert space. The traces also enter the coefficients of the characteristic polynominal of the Floquet operator. Statistical properties of these coefficients give rise to a new criterion for the distinction of chaos and regular motion. 相似文献
20.
COHERENT INFORMATION ON THERMAL RADIATION NOISE CHANNEL: AN APPROACH OF INTEGRAL WITHIN ORDERED PRODUCT OF OPERATORS 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An analytical expression is given to the coherent information of the thermal radiation signal transmitted over the thermal radiation noise channel, one of the most essential quantum Gaussian channels. Focusing on the single normal mode of the thermal radiation signal and noise, we resolve the entangled state density operator, which characterizes quantum information transmission, into a direct product of two parts, with each part being a thermal radiation density operator. The calculation is aided by the technique known as "integral within ordered product of operators". 相似文献